Traffic signals have long been used to regulate the flow of traffic at intersections. Generally, traffic signals have relied on timers or vehicle sensors to determine when to change the phase of traffic signal lights, thereby signaling alternating directions of traffic to stop, and others to proceed. This situation is commonly exemplified in an emergency-vehicle application.
Emergency vehicles, such as police cars, fire trucks and ambulances, are generally permitted to cross an intersection against a traffic signal. Emergency vehicles have typically depended on horns, sirens and flashing lights to alert other drivers approaching the intersection that an emergency vehicle intends to cross the intersection. However, due to hearing impairment, air conditioning, audio systems and other distractions, often the driver of a vehicle approaching an intersection will not be aware of a warning being emitted by an approaching emergency vehicle.
Municipalities that use traffic preemption systems generally also have mass-transit capabilities as well, such as bus systems, trolley cars, or other people moving capabilities. Mass-transit systems present their own problems in the areas of traffic control and scheduling of large numbers of transit vehicles. As traffic and congestion increases, it becomes more difficult to maintain schedules for mass-transit vehicles that share resources with the public, such as roadways. As the population expands, these abovementioned issues may increase.